Publication Date

2014-04-06

Availability

Open access

Embargo Period

2014-04-06

Degree Name

Master of Science (MS)

Department

Meteorology and Physical Oceanography (Marine)

Date of Defense

2014-04-03

First Committee Member

Amy C. Clement

Second Committee Member

Brian J. Soden

Third Committee Member

Larry C. Peterson

Abstract

The response of tropical precipitation to precessional forcing is investigated using idealized precession experiments from two climate models as well as mid-Holocene experiments from ten climate models participating in the Paleoclimate Modeling Intercomparison Project Phase III. The objectives of this thesis are to analyze an energetic mechanism that describes precessional changes in precipitation and determine if this mechanism is sufficient for explaining changes in precipitation over land and ocean. Both mid-Holocene experiments and idealized experiments show a seasonal land-sea asymmetry in tropical precipitation that cannot be explained simply by monsoon dynamics. Instead, this shift in precipitation is interpreted using an energetic framework that describes how changes in the net top-of-atmosphere radiation affect the atmosphere and surface energy balances. Over land, changes in precipitation can be explained through changes in moist static energy flux divergence, but over the ocean, the moist static energy flux divergence plays a lesser role because the surface energy balance compensates for the majority of the change in top-of-atmosphere radiation. Because this mechanism does not sufficiently describe why precipitation changes over the ocean, we break down the dry and moist energy responses of the atmosphere in order to further explain this process. We find that the atmosphere’s response to precessional forcing over land drives changes in circulation, which influence the thermodynamic structure of the atmosphere over the ocean, ultimately allowing for precipitation changes over the ocean. To conclude, we examine the regional changes in precipitation in the tropical Atlantic and over Africa, and we discuss how paleoclimate records from this region can be used for model verification.

Keywords

Precession; Precipitation; Monsoon; Orbital cycles; Paleoclimate

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